Upgrade notes for vector store delete API breaking change

Signed-off-by: Soby Chacko <soby.chacko@broadcom.com>

spring-ai-docs/src/main/antora/modules/ROOT/pages/upgrade-notes.adoc

@@ -64,6 +64,27 @@ Spring AI updates to use Spring Boot 3.4.2 for the dependency management. You ca
 * If you are upgrading to Spring Boot 3.4.2, please make sure to refer to https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.4-Release-Notes#upgrading-from-spring-boot-33[this] documentation for the changes required to configure the REST Client. Notably, if you don’t have an HTTP client library on the classpath, this will likely result in the use of `JdkClientHttpRequestFactory` where `SimpleClientHttpRequestFactory` would have been used previously. To switch to use `SimpleClientHttpRequestFactory`, you need to set `spring.http.client.factory=simple`.
 * If you are using a different version of Spring Boot (say Spring Boot 3.3.x) and need a specific version of a dependency, you can override it in your build configuration.
 
+=== Vector Store API changes
+
+In version 1.0.0-M6, the `delete` method in the `VectorStore` interface has been modified to be a void operation instead of returning an `Optional<Boolean>`.
+If your code previously checked the return value of the delete operation, you'll need to remove this check.
+The operation now throws an exception if the deletion fails, providing more direct error handling.
+
+==== Before 1.0.0-M6:
+[source,java]
+----
+Optional<Boolean> result = vectorStore.delete(ids);
+if (result.isPresent() && result.get()) {
+    // handle successful deletion
+}
+----
+
+==== In 1.0.0-M6 and later:
+[source,java]
+----
+vectorStore.delete(ids);
+// deletion successful if no exception is thrown
+----
 
 == Upgrading to 1.0.0.M5